Principal Investigator / Author(s): Keith D. Stolzenbach

Contractor: UC Los Angeles

Contract Number: 04-345

A particle tracer methodology based on the use of Neutron Activation Analysis (NAA) to detect concentrations of rare earth elements sorbed to porous silica particles appears to be a promising technique for studying the transport of aerosols and resuspended particulates and the consequent effects on air and water quality and human health. Following an investigation of alternative techniques for labeling, deploying, and recovering the tracer, the feasibility of the NAA methodology was investigated in field experiments designed to measure the resuspension of particles by wind and the resulting deposition on downwind surfaces. All of the basic components of the NAA tracer performed as expected, including the ability of the technique to distinguish between the transport of silica of different sizes labeled with different rare earths. Measured particle resuspension was characterized by rapid initial loss of tracer when first exposed to wind, by a persistent level of tracer sequestered from resuspension, and by almost no dependence on meteorological conditions. The detection of deposited tracer material diluted during transport in the air was severely limited by the level of rare earth labeling achieved in the silica and by higher than expected background levels of rare earth concentrations in silica, sample vials, and natural particulates. The result of this study suggest that the NAA tracer technique can be applied quantitatively at reasonable cost per sample in field scale studies, but that the method is primarily useful in studying particle resuspension from surfaces. The results of the study also indicate that resuspension of particles in the size range used in this study (10 ~ 60 μm) is significant relative to rates of redeposition and that such particles are highly mobile.